Learning and behavior problems among US children appear to be rising steadily, however the etiology for these behavioral changes is unknown. Exposure to low-levels of various neurotoxins has been suggested as a potential factor in these changes. For example, low levels of lead are known to be associated with learning deficits and social behavior problems. One issue with animal models for the effects of various neurotoxins is that they are limited to investigating only one factor even though human exposures occur together with many other environmental factors. For example, it is known that there is a differential exposure to heavy metals in low social economic status households. Therefore, we will investigate the effects of lead and manganese (since manganese is known to potentiate the increase in the amount of lead that accumulates in the brain) in combination with stressors (isolation, overcrowding, or limited resources with maternal depression) to mimic human conditions. The first aim is to determine which stressor has the greatest impact on heavy metal exposure by measuring physiological parameters during the period of administration as well as investigating the long-term effects of this combination on neurotransmitters and long-term potenitation induction. The second aim is to investigate the dose-dependency of lead or manganese in combination with stress on the learning ability and social aspects of the animals. We will be using a novel approach to investigating learning and memory in these animals by using a combination of learning tests that test different types of learning. This is relevant to how humans would have to learn as well. This aim will provide a foundation to model low level exposure and to understand the functional changes that occur. The third aim is to combine lead, manganese and stress and assess the impact of this more relevant combination to human exposures on learning and memory and social behavior. The last aim is designed to investigate the developmental changes that occur related to the three combination exposure by using MRI as well as looking at the nuerophysiological response when the animals are adults. These studies will provide much needed data on the low-level effects of neurotoxins in combination with environmentally relevant stressors. Potential mechanisms will be explored by investigating neurotransmitter and neuroendocrine systems and the glutamate receptor complex.